Spacer grid for heat exchange elements with eddy diffusion promotion means

ABSTRACT

A spacer grid of cellular form for an assembly of elongate heat exchange elements has projections in each cell for locating the elements. The cell defining walls of the grid have irregular edges on one side of the grid for promoting eddy diffusion in coolant passing through the grid. The irregular edges may be formed by sections defined by slits or incisions in the edges and deformed out of the planes of the cell-defining grid walls.

Inventors 'Anp'LNo. I Filed I Patented Aisignee aritm't i, United- States Patent Colh loomun Altrlnghun;

Colin Bette, Hale, both 01, England 817.329

A r. 18, I969 June 29, I97] uimm Kingdom Atomk' Energy Authority London, Engine! Nov. 23g

Greet Blihh cuts-umoga lauu'n See. No." 594,168, Nov. 14, 1966, now Patent No. 3,439,737, died Apr., 1969.

SPACER GRID FOR HEAT EXCHANGE ELEMENTS WITH EDDY DIFFUSION PROMOTION MEANS I ChhJDnwfngFip.

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[56] References Cited I UNITED STATES PATENTS 3.344.855 10/1967 C1ark 176/78 X 3,356,582 12/1967 Saunders. 176/76X 3,395,077 7/1968 Tong et al. 176/78 3.439.737 4/1969 Boorman et a1. 167/109 FOl'lElGN PATENTS 1.085.976 7/1960 Germany 176/73 Pnrnqry Examiner-Albert W. Davis, Jr. Attorney-Larson and Taylor ABSTRACT: A space: grid ot'cellular form for an assembly of elongate heat exchange elements has projections in each cell for locating the eiements. The cell defining walls of the grid have in'egular edges on one side of the grid for promoting eddy difluiion in coolant passing through the grid. The in'egu 1a: edges may be formed by sections defined by $111: or incisions in the edges and deformed out of the planes of the celldefining grid walk.

" zcaoss-amscnccionmrsoamnmn 3339.737. 68nd Apr. Z Z. i981 prise sections of cell wall which are I sembl'y, I ingthc'grids; Whereas coolant flow through a nuclear fuel us- .vention.

lsaizgappticntlrmofapplication I seem, sums. nun rut. NJ? M 0.; at u r I I sncttonoouo cirrus INVENTIQN invention relates to murder heat eschange elemeats and is particularly applicable to nuclear reactor fuel asaentblies such as comprise a plurality of fuel rods clustered in spaced array.

will lnh nuclear reactor fuel assembly the, kind mentioned.

above the fuel rods are usually end from another at intervals along their length by transverse spacergrldsnPreviously' proposed spacer grids have been of cellular foirn; penetrated by the fuel rods. and designed to restrain radial deflection of the fuel rods. in use of such nuclear fuel "usemblics in a nuclear reactor it is customary to cool'the assemblies by means of a stream of coolant which passes longitudinally the fuel rods.

SlJMMARY OF The INVENTION In accordance with the present invention, a spacer grid for an assembly of elongate heat exchange elements clustered in spacedarray with individual axes parallel is of cellular form. and cells of the grid each have projections which are adapted to engagc and thereby locate, an elongate heat exchange element extending through the cell, and an irregular edge provided on one side of the grid for promoting eddy diffusion in coolant passing through the gridQThe irregular edge 'may comdefined by incisions and deformed out ofthe plane of the wall.

. The arrangement provides for efficient heat transfer between the elements and coolant through the promotion of turbulence by eddy diffusion in the coolant flow stream. The deformed edge or edges may be on the downstream side of the grid relative to the direction of coolant flow through the asthusprotnoting eddy diffusion in the flow'stream leavsernbly withn conventional cellular spacer grid tends to be in channelsbetwecn and defined by the fuel rods, the turbulence by eddy diffusion which is promoted by the spaccrgrid of the instant invention is considered advantageous from the point of view of heat transfer considerations in that it helps reduce hot channel factors arising from geometrical tolerances and local fuel element variations. and also helps reduce coolant outlet temperature gradients arising from heat flux gradients in the assembly. without a prohibitive increase in the pressure drop experienced by the coolant. Although not necessarily, the locating projections may be shaped and arranged so as to imsupported and spaced one upper and lower ends 23, 24. respectively,

part to the coolant flow stream a rotational component of I flow.

. BRIEF DESCRlPTlON OF THE DRAWINGS I in the accompanying exemplifying drawings FIG. 1 is s part-sectional elevation of a nuclear reactor fuel assembly in accordance with the invention.

' FIG. 2 is an enlarged plan view of a part of FIG. 1.

FIG. 3 is a fragmentary view in the direction of arrow ll! of DESCRIPTION or THE PREFERRED EMBODIMENT FIG I shows it nuclear reactor fuel assembly comprising a plurality of elongate fuel rqds'lo clustered in'spaced array with their longitudinal axes parnllelwithin a casing or wrapper llof wsnnatcrcmseetilrm structure of one of the which illustrates the upper edge .of one of the to say the downstream edge relative to the direction ofcoolant cttheirlppasenbbyanupparsupponpiateli eodstlaslbelrodslu unsrrmtmmnu mmr spaced out from another at intervais'aloogthelrleagthbym sraespaoergrids Id ticnetratedbytherodsl'sndsscuredtothewrapper ll.Thc grids N are ofcellular form. each an outer he agonal frame t5 aecuredto the rapper ll. lnuae ofthe illustrated fuel aaiernbly in a nuclear reactor the fuel rods 10 are cooled by a stream of coolant which passes longitudinally over the rodnasindicatedbyarrovs l6.

FlG. 2 shows'strips 17 of hexagonal-meander shape which are joined'together to define hexagonal cells'lb forming a cell spacer grids I. it being understood that the strips 17 are joined at their ends to oneof the frames l5 shown in H0. l. Each cell 18 is penetrated by one fuel rod l0 containing fissile material l9 such as. for example. a mixture of uranium and plutonium oxides enclosed in a plain tubular sheath 20 constructed of stainless steel.

Referring to FIG. 3 in conjunction with FIG. 2, the strips 17 are formed with projections 21 so that each cell 18 has three such projections 2i directed inwardly into it and disposed on alternate ones of its six wallsZZ. in contrast to conventional cellular spacer grids having projections of circular form (oflen referred to as dimples),.thc projections 21, in their illustrated form, are elongated and are inclined with respect to the axis of the fuel rod engaged thereby. In other words, each of the projcctions 2i slopes in extending from a lower to an upper region of its wall-22 Each of the projections 21 has rounded and is symmetrically disposed with respect to its wall-22. In each cell 18 the three projections 2| are similarly orientated. andthe fuel rod 10 penetrating that cell is located by point contact of its unribbed sheath 20 with the projections 21 at these circumferentially equispaced positions.

I To cause and enhance mi ling of coolant. turbulence by eddy diffusion is promoted in the coolant flow stream by an irregular edge provided on one side of the grid. An exemplary structure for, accomplishing this purpoae is shown in FIG. 4, strips 17 (that is flow through the assembly) as being made irregular by having sections 28 curved in one direction (toward but clear of one of the fuel rods), alternating with sections 29 curved in the opposite direction (away from but clear of the fuel rod). the sections being defined by vertical slits or incisions in the upper edge.

In operation. coolant flowing upwardly as indicated by the arrows i6 is deflected by the projections 21 and the edge sections 28 and 29. and thus has imparted 'to it in each cell 18 a rotational component of flow as indicated by arrows 25. as well as turbulence in the form of eddy dilfusion in the flow stream leaving the grids 14. in this way the projections and the irregular edge sections promote coolant swirling or mixing in the coolant flow stream passing through the grids 14. which is considered advantageous for the reasons given above. The strips are arranged edge on to the coolant flow through the assembly, and the pressure drop experienced by the coolant is not prohibitively increased as compared with conventional spacer The components to 14 are typically constructed from stainless steel. and the projections 21 are conveniently formed by stamping or slotting of the strips 17. Purely by way of illustration. mention is made that for a depth D of spacer grid as represented byarrow 26 in FIG. 3. the projections 21 typically may have a length of DB as represented by arrow 27 in FIG. 3 and be disposed at an angle of 20 as represented by the included angle between the arrows 26. 2'1. The irregular edge as illustrated in F10. 4 is, of. course. formed by-the sections 28 and 29 being deformed out of the plane of the wall. the sec tions being defined by vertical slits or incisions in the edge 1 3 -Thus. fabrication of the improved spacer grid poses no problem;

l. A spacer grid for an as mbly of elongate heat exchange elernenu cluttered'in spaced array with individual axes paral- 5 el,- the grid having cells bounded by joined strips within a peripheral fra'me. each cell having projections which are adapted to "engage, and thereby locate. an elongate heat exchange element extending through the cell, the grid having an irregular edge on one face ride for promoting eddy diffusion in coolant passing through the grid, said irregular edge comprising lide-by-side sections defined by llits extending from one edge of the joined ltripe and said section: being deformed out of the plane of said face side of the grid alternately in opposite directions. 

1. A spacer grid for an assembly of elongate heat exchange elements clustered in spaced array with individual axes parallel, the grid having cells bounded by joined strips within a peripheral frame, each cell having projections which are adapted to engage, and thereby locate, an elongate heat exchange element extending through the cell, the grid having an irregular edge on one face side for promoting eddy diffusion in coolant passing through the grid, said irregular edge comprising side-by-side sections defined by slits extending from one edge of the joined strips and said sections being deformed out of the plane of said face side of the grid alternately in opposite directions. 